An electrophoretic display (EPD) is a non-emissive device based on the electrophoresis phenomenon influencing charged pigment particles suspended in a colored dielectric solvent. This type of display was first proposed in 1969. An EPD typically comprises a pair of opposed, spaced-apart plate-like electrodes, with spacers predetermining a certain distance between the electrodes. At least one of the electrodes, typically on the viewing side, is transparent.
When a voltage difference is imposed between the two electrodes, the pigment particles migrate by attraction to the plate of polarity opposite that of the pigment particles. Thus, the color showing at the transparent plate, determined by selectively charging the plates, can be either the color of the solvent or the color of the pigment particles. Reversal of plate polarity will cause the particles to migrate back to the opposite plate, thereby reversing the color. Intermediate color density (or shades of gray) due to intermediate pigment density at the transparent plate may be obtained by controlling the plate charge through a range of voltages or pulsing time.
EPDs of different pixel or cell structures have been reported previously, for example, the partition-type EPD (M. A. Hopper and V. Novotny, IEEE Trans. Electr. Dev., Vol. ED 26, No. 8, pp. 1148-1152 (1979)) and the microencapsulated EPD (U.S. Pat. Nos. 5,961,804 and 5,930,026).
An improved EPD technology was recently disclosed in U.S. Pat. Nos. 6,930,818, 6,672,921 and 6,933,098, all of which are incorporated herein by reference. The improved EPD comprises isolated cells formed from microcups of well-defined shape, size and aspect ratio and filled with an electrophoretic fluid comprising charged particles dispersed in a dielectric solvent. The filled cells are individually sealed with a polymeric sealing layer, preferably formed from a composition comprising a material selected from the group consisting of thermoplastics, thermosets and precursors thereof.
The microcup wall in fact is a built-in spacer or support to keep the top and bottom substrates apart at a fixed distance and provides superior mechanical properties and structural integrity. Since the display fluid within the display prepared by the microcup technology is enclosed and isolated in each cell, the microcup-based display may be cut into almost any dimensions without the risk of damaging the display performance due to the loss of display fluid in the active areas.
The microcup structure also enables a format flexible and efficient roll-to-roll continuous manufacturing process for EPDs, particularly for thin, flexible and durable EPDs. The displays can be prepared on a continuous web of a conductor film such as ITO/PET by, for example, (1) coating a radiation curable composition onto a conductor film (i.e., ITO/PET film), (2) forming the microcup structure by a microembossing or photolithographic method, (3) filling the microcups with an electrophoretic fluid and sealing the filled microcups, (4) laminating the sealed microcups with a second conductor film and (5) slicing and cutting the display into a desirable size or format for assembling. To complete the construction of a display device, the electrode lines of the display must be exposed and connected to a driver circuitry.
However, not all electrode designs are suitable for use in a roll-to-roll format flexible manufacturing process. In fact, implementation of the roll-to-roll process is severely limited by the design of the electrodes (and, if present, also the via holes and trace lines) connecting to a driver circuitry. To enable a roll-to-roll format flexible process, the electrodes and connecting traces require special designs. However, the pitch sizes of the electrode lines of the specially designed electrodes very often are not compatible with those of the commonly used drivers. Consequently, an expensive fan-in/fan-out flexible circuitry is typically needed as an adapter to bridge the electrode lines and the driver circuit. Bonding the fan-in/fan-out flexible circuitry to both the display panel and the driver is an expensive and time-consuming process.
Accordingly, in order to reduce the cost of manufacturing and maintaining display modules which typically comprise a display panel, driver and necessary circuitries, there is a strong need for a system which is more reliable, easier to install and maintain and suitable for roll-to-roll format flexible manufacturing.